Conventionally, when driving a motor using an inverter, in order to reduce noise of the motor generated with switching of a transistor, carrier frequency of the inverter is set high. When the carrier frequency is set high or a source voltage is high, a potential difference between an inner ring and an outer ring of a rolling bearing which supports a shaft becomes large, and thus electric current easily flows into the rolling bearing. There is a problem that the electric current flowing through the rolling bearing generates corrosion so-called electric corrosion on rolling surfaces of both races of the inner ring and the outer ring and a rolling element (balls or rollers rolling between the inner and outer rings), thereby degrading the durability of the rolling bearing. Further, there is another problem that large noise may occur from the motor due to the generation of the electric corrosion. Various kinds of motors which solve the above problems have been proposed.
For instance, a motor has been proposed, which is structured by a stator core; a stator molded to form one body with a stator winding wound to the stator core using insulating resin; a rotor having a shaft; a first bearing and a second bearing for supporting the shaft; a metal bracket coupled to the stator and retaining at least either of the first bearing and the second bearing; and a conductive member for short-circuiting the stator core and the metal bracket (for instance, refer to Patent Literature 1).
Further, another motor has been proposed, in which a bracket of an output side and a bracket of the opposite side to the output side attached to a frame is short-circuited by a conductive tape, and the conductive tape is bonded to the outside of the frame (for instance, refer to Patent Literature 2).